Studies were carried out on adoptive tumor immunity in naive guinea pigs that received specifically sensitized spleen cells from hyperimmunized donors. The effector spleen cells were also tested for their capacity to kill the tumor target cells in vitro. Tumor resistance in vivo increased experimentally as a function of the number of intravenously transferred sensitied spleen cells. Within the tumor challenge doses analyzed, suppression of tumor growth by adoptive immunity appears to be independent of specific immune response in the recipient. Studies on distribution and expression of antitumor immunity after intravenous infusion of immune cells revealed that the transferred immunity was distributed randomly throughout the skin of the recipient and there was no evidence indicating that they are attracted specifically to the tumor inoculation site.